One of the most common types of bone fractures that occurs in humans is a fracture of the distal radius. In repairing these fractures, it is desirable to set the components of the fractured bone in a proper alignment, and to thereafter immobilize the bone to prevent relative movement between the fractured components during a period of healing. While it is desirable to immobilize relative movement between the fractured bone components during the bone healing period, it also is highly desirable to maintain, and indeed to promote, movement of the adjacent wrist joint during this same period. In order to achieve these seemingly inconsistent objectives, several types of fixation devices have been developed.
The prior art fixation devices for immobilizing the fractured components of the radius bone have been of two general types, external and internal. Although external fixation devices have been found to be effective in certain instances for specific kinds of fractures, they are aesthetically objectional to many people, and are prone to numerous complications, such as infection at the pin sites.
One prior art internal fixation device for immobilizing distal radius fracture components is described in U.S. Pat. No. 5,006,120 to Carter. This device uses a side plate that is secured to the dorsal portion of the radius by a plurality of screws. The Carter plate supports a plurality of attachable U-shaped blades at one of its longitudinal ends. These U-shaped blades are placed in a correspondingly U-shaped groove cut through the fractured components, and the blades are thereafter threadably secured to the plate.
While the internal fixation device of the above-referenced patent offers a number of advantages, it also is incumbered with a number of disadvantages. For example, the Carter plate is generally planar, and its use is limited to the dorsal portion of the distal radius bone. However, such a position is inappropriate for the more commonly oriented fractures which extend in a direction transverse to that plate. In addition, the U-shaped blades disclosed in this patent, which are attachably secured to the plate, are capable of movement relative thereto, especially when substantial stress is applied to that area of the body. Any such relative movement between the blades and the side plate, of course, permits corresponding relative movement between the fractured bone components. Moreover, exercise of the wrist, which most desirably and advantageously produces synovial fluid and lubricates the cartilage during the bone healing process, produces substantial stress on a distal radius bone. For example, gentle movement of the wrist can produce pressures in the range of 20 pounds per square inch, while squeezing with the hand to make a fist can produce pressures in the order of 120 pounds per square inch.
It is also highly advantageous, when securing fractured bone segments in their anatomically correct positions, to attach the fixation apparatus to the cortical portion of the bone. Unfortunately, this cortical portion is relatively thin, in the order of 2-3 mm in thickness, and the positioning and securing of a fixation apparatus into the relatively thin layer of cortical bone or into the mineral dense juxta-articular cancellous bone is quite difficult.